This invention relates to mixing apparatus, and more particularly mixing apparatus of a type employed to mix fluids together in a desired ratio.
Mixing apparatus are frequently employed in offset printing press operations where it is desirable to apply a mixture of etch concentrate dissolved in water to the nonprinting portions of a printing plate mounted on a plate cylinder. Damping rollers, which roll through a fountain pan filled with the mixture, apply it to the printing plate. The quality of printed material produced will depend upon the accuracy with which the mixture may be regulated to correspond to different ink or paper types.
In the past, some mixing apparatus have utilized a bypass conduit arrangement in combination with a main conduit wherein a number of eductors, a series of conduit restrictions, and/or a system of valves were required to effectuate accurate proportional mixing of two fluids. The first fluid was forced into the bypass conduit in such prior structures, due to valve or restriction arrangements, and would flow through an eductor disposed within the bypass conduit thereby causing a second fluid to be drawn into the first fluid and become premixed prior to being further mixed with the first fluid flowing into the main conduit. With such prior structures, when it was desired to increase the proportionate amount of second fluid to be mixed with the first fluid, flow of the first fluid through the main conduit had to be restricted (i.e., by a valve) so that a larger head pressure would be built up in the bypass conduit, thereby increasing the lifting suction generated by the eductor located therein, while at the same time restricting the amount of first fluid flowing through the main conduit. Thus, such prior apparatus depended upon critical relationships of fluid pressures, in order to attain the desired mixing ratio of the fluids which necessitated additional components such as an eductor in the bypass conduit.
Other mixing apparatus either relied upon a gravity feed system thereby restricting the location of the apparatus; mix the fluids together in a fixed predetermined ratio and then accumulate same in a storage reservoir or the like; or introduce a second fluid in an undiluted state directly into the main fluid conduit, with or without employing an eductor. Thus, the prior mixing apparatus were complicated in design often requiring a multiplicity of parts, both electrical and mechanical, and were costly and difficult to manufacture and service.